In the prior art, pressure atomizing fuel nozzles of various types have been employed to inject fuel into the combustion air. Neither the air nor the fuel has been heated beyond what occurs by air compression. As a result, fuel combustor engines of the prior art have idle combustion efficiencies generally below 100%, some being as low as 60%. Low combustion efficiencies result in high exhaust emissions of carbon monoxide and unburned hydrocarbons.
Some attempts have been made to improve engine efficiency by using heat pipes to heat the incoming fuel prior to the injection thereof into the combustor, for example, as in U.S. Pat. No. 3,842,596 to Gray, employing heat exchangers in hollow turbine blades, wherein the collected heat is transferred to the incoming fuel to preheat it; or in U.S. Pat. No. 3,710,572 to Herud, which employs graphite filaments which act to conduct heat away from the combustion chamber, and wherein said heat is employed to preheat the incoming fuel and air.
The U.S. Pat. to Marek No. 4,052,144 discloses a fuel combustor having a chamber with air and fuel inlets and a combination of gas outlets, and of which the present invention is an improvement.
Various prior U.S. patents, in addition to those noted above, dislose engines having heat exchangers for preheating fuel and air, employing suitable heat exchange media, such as sodium. Thus, attention is invited to the following U.S. Pat. Nos.: Adams et al 3,024,606; Beam 3,355,883; Pravda 3,621,908; Wolf et al 3,733,826; and Koch 3,895,488.
The heat transfer arrangements of the prior art have serious disadvantages. One such major disadvantage is that the heat transfer element is responsible for causing excessive quenching of the combustion. Another serious disadvantage is that in some of the prior art systems where the fuel and air are not kept separate, auto-ignition occurs during preheating. Also, undesirable coking of the fuel on the heat pipe may occur, which causes interference with the transmission of heat.
Another disadvantage of prior art fuel-air preheating arrangements is that conventional cooling methods are employed, such as lines located downstream of the primary combustion zone. This makes it possible for quenching of combustion reactions to occur in these downstream regions, thereby causing incomplete combustion of the fuel.